A. Control of gastric acid hypersecretion in patients with Zollinger- Ellison syndrome (ZES). 1. The recommended maintenance doses of Na+-K+ ATPase inhibitors was shown to be too high and by using lower doses savings of up to $6,000/year in medication expenses can be obtained. 2. An analysis of 10-years of continuous treatment with omeprazole in patients with ZES was reported. It was concluded the drug is safe and effective even with prolonged usage. 3. Lansoprazole, a new H+-K+ ATPase inhibitor was shown to be safe and effective and have a prolonged duration of action, therefore will be useful in patients with ZES. 4. Postcurative resection patients with ZES had a marked decrease in basal acid secretion, however 67% remained mild hypersecretors and will require continued low dose treatment. B. Studies related to tumor localization, surgery, treatment of advanced disease. 1. In a prospective study it was shown that both fasting gastrin levels and secretin provocative tests need to be done to predict cure. Imaging studies and calcium provocative studies are not necessary. 2. Gastric carcinoid tumors were shown to be best identified by fine needle aspiration, rather than biopsy in hypergastrinemic patients. 3. In a collaborative study with the Pathology Department (NCI) flow cytometry results of gastrinomas were shown to correlate independently with the disease extent. 4. Prospective studies with the Radiology Department demonstrated that MRI was now the best noninvasive method to localize metastatic gastrinoma to the liver in patients with ZES. The use of intra-arterial secretin with gastrin sampling was shown to be superior to portal venous sampling to localize gastrinomas. 5. A prospective study with the NCI Surgery Branch, demonstrated that duodenotomy was required to localize primary duodenal gastrinomas. 6. Interferon was shown to have limited efficacy in the treatment of metastatic gastrinomas.